Abnormal esophageal sensations, such as esophageal-related noncardiac chest pain and heartburn, are common complaints. The underlying mechanism of such esophageal nociception remains unclear. The long-term goal of our research is to elucidate the peripheral mechanism of esophageal inflammatory nociception. This proposal focuses on peripheral sensitization of vagal sensory afferents in our guinea-pig ex vivo esophageal-vagal preparation. Using this model, we have established the first direct evidence that activation of mast cells sensitizes the esophageal vagal afferent C-fiber and results in increased nerve excitability. Preliminary studies have demonstrated that several mediators and certain downstream ion channels are involved in this sensitization process. This proposal focuses on the interaction between esophageal mast cell and sensory afferent nerves. Our specific hypothesis is that mast cells in the esophageal wall play a central role in sensory neuro-modulation. Our published studies demonstrated that 1) esophageal mast cells are mainly distributed along the lamina propria with three immuno-subsets and can be activated by IgE-dependent in vitro antigen-challenge; 2) activation of esophageal mast cells increases the excitability of vagal nodose nociceptive C fibers; 3) mast cell preformed mediators histamine and tryptase participate in this sensitization process; and 4) sensitization of downstream TRPA1 by mast cell activation plays an important role in the modulation of nodose C fiber nerve activity. The proposed studies in the present application build on these published results and additional preliminary data to further investigate esophageal mast cell-nerve interactions. Our specific aims are: 1) determine esophageal mast cell activation by non-IgE-dependent stimuli such as protons, neuropeptides, and certain cytokines; 2) define the full range of subtypes of esophageal vagal nociceptive afferent nerves in response to MC activation; 3) clarify the roles of MC mediators in activating/sensitizing esophageal vagal sensory afferent nerve subtypes; and 4) determine the downstream key ion channels in MC-mediated nociceptor sensitization, with a focus on TRPA1. The results of this study will advance the understanding of the role esophageal mast cells nerve interactions in peripheral nociceptor sensitization and will contribute to expanding therapeutic approaches to esophageal inflammatory nociception.